The brake lever is mechanically connected to both rear brake housings by rods and levers. On the side of the transmission, the brake lever attaches to a rod that travels straight back towards the rear of the truck. At the cross member that has the hanger bearing for the driveline, there is a lever mounted that connects this rod, and to two separate rods on each side of the truck to connect to the flexible cables that run down to each side of the axle. the other end of the flexible cables ties into the actuator arm that sticks out of the brake drum. There is also a return spring that is connected to the central lever that hooks via a long rod into the crossmember just in front of the rear axle. There is also a support loop to keep the long rod between the transmission and the central lever from sagging excessively.
Pulling the lever back in the cab causes the rods under the truck to move forward, pulling on the cables to each wheel and applying the brake shoes to the drum. Adjustment is accomplished by changing the length of the various rods by turning a clevis on a threaded portion of the rod. The other end of the rods have a fixed clevis. Hopefully these photos help, I didn't want to get dirty crawling on the floor when I took them a few minutes ago.
